Scientists in Whangarei are carrying out comprehensive physical testing and full medical exams checking smell, hearing, vision, and even anxiety.

And fish are the subjects.

Niwa's Northland Marine Research Centre in Bream Bay is the site for an experiment looking at the effects of ocean acidification, when carbon dioxide is dissolved into the sea therefore changing the pH level, and warmer sea temperatures on snapper larvae.

"To be able to look at the effects of climate change on such a highly valued commercial, customary and recreational species as snapper in New Zealand is a first for us and very exciting," said Niwa marine ecologist Darren Parsons.

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The experiment is a collaboration between Niwa, Phillip Munday of James Cook University in Australia, and the University of Auckland.

The snapper experiment began last month when adult broodstock spawned and the eggs placed in tanks under four different conditions

In one set of tanks the temperature is 18C which matches normal conditions at the time of spawning. In other tanks the temperature is 22C which is closer to sea surface temperatures reached this summer.

In the third set of tanks carbon dioxide levels are kept at current oceanic levels and in the fourth the levels are raised to match those expected at the end of this century.

Each tank was stocked with thousands of eggs.

During the first 35 days, after the eggs hatched into larvae, scientists monitored how fast they grew, photographed them, and counted how many died - that data has not been analysed yet.

The scientists are also watching changes in the behaviour of the fish.

For example, fish will normally swim away from water if they can smell a predator nearby. But when that water is treated with high CO2, some other species have been shown to swim towards it.

Dr Parsons said to test the behaviour of snapper they put the fish in a chamber which has two water sources - one from the water the fish was raised in, and the other from a tank that had hapuka in it.

"The fish raised under ambient conditions showed a reasonably strong response where they would avoid the water that had been flowing over hapuka.

"For the fish that had been reared under the higher CO2 conditions, it's really early stages, but it looks like it doesn't change their behaviour."

Meanwhile in a flume tank, which is like "treadmill for fish", larvae were tested for how well they swim.

"We ramp up the speed of the treadmill until the fish can't swim forward anymore to give us an idea of their aerobic performance and how this differs for larvae from the different experimental conditions."

Vision and hearing tests are also conducted as well as anxiety tests.

"This is a start at figuring out the scale of the issues and how they might unfold over time."